The invention relates to a pickoff or signal generator and more particularly to such a pickoff for use in transducing mechanical motion to electrical output.
Electrical pickoffs for use in transducers for transposing mechanical motion to electrical output are known in the art and may take the form of potentiometers, inductive pickoffs, capacitive pickoffs, piezoelectric pickoffs or any one of a wide variety of other pickoffs for sensing a mechanical quantity and transposing it to an electrical signal. Such pickoffs utilizing AC signals are desirable because they obviate the need for sliding mechanical contacts and attendant noise associated therewith. Other sources of noise are also more easily suppressed through the use of AC pickoffs. Variable C type pickoffs are known wherein a separate oscillator is utilized and coupled through two or more secondaries to series resonant circuits having inductors therein with a moving conducting member configured for mechanical motion relative to the inductors. The problems with these latter types of circuits involve the necessity for RF type transformers precluding any possibility of miniaturized hybrid pickoff circuitry. These circuits have limited gain potential which has an effect on the dynamic range obtainable. Moreover, a variable q type pickoff having a separate oscillator circuit and two series tuned inductive capacitive resonant circuits requires a great deal of adjustment at high oscillator frequencies due to stray capacitance and interaction between the resonant circuits.
There is a need, therefore, for a variable Q type pickoff which is capable of being hybridized, requires little adjustment time during assembly, and is more efficient allowing higher gain to be provided by the pickoff circuit itself and consequent enlargement of dynamic range.